For some years, different types of radio networks for wireless communication have been developed to provide radio access for various wireless devices. The radio networks are constantly improved to provide better coverage and capacity and to meet the demands from subscribers using increasingly advanced services and equipment, e.g. smartphones and tablets, which may require considerable amounts of bandwidth and resources for data transport in the networks. A limiting factor for capacity of a radio network is the amount of available radio resources, e.g. in terms of time, frequency bandwidth and transmit power, and the capacity of a radio network is improved by more efficient usage of such radio resources.
In this disclosure, the term “wireless device” is used to represent any communication entity capable of radio communication with a radio network by sending and receiving radio signals, such as e.g. mobile telephones, tablets, laptop computers and Machine-to-Machine, M2M, devices, also known as Machine Type Communication, MTC, devices, Laptop Embedded Equipped, LEE, Laptop Mounted Equipment, LME, USB dongles, Customer Premises Equipment, CPE, etc. An MTC device may also be referred to as a low complexity and/or low cost UE. The term MTC device will be used herein for consistency although it could be replaced by M2M device throughout this disclosure. Another common generic term in this field is “User Equipment, UE” which is frequently used herein as a synonym for wireless device. Further, the term “network node”, is used herein to represent any node of a radio network that is operative to communicate radio signals with wireless devices, or to control some network entity having radio equipment for receiving/transmitting the radio signals.
The network node in this disclosure could also be referred to as a base station, radio node, e-NodeB, eNB, NB, base transceiver station, access point, relay node, Remote Radio Unit (RU, Remote Radio Head, RRH, etc., depending on the type of network and terminology used. Both terms network node and base station are used interchangeably in this disclosure.
Further, the term “radio node” is used herein to represent any of a network node and a wireless device. Thus, when it is said that a first radio node transmits data to a second radio node, this could be valid for downlink transmission when a network node in a wireless network transmits data to a wireless device, and for uplink transmission when a wireless device transmits data to a network node, and also for Device-to-Device, D2D, transmission when a wireless device transmits data to another wireless device. In this description, it is further said that the data is transmitted as a “data block” although the description is not limited to any particular format or technology used for realizing the data block.
It is becoming increasingly common to employ MTC devices at certain locations to operate automatically by sending data and receiving control signals according to some predefined behavior. Such MTC devices may be configured to measure and report some metric or parameter of interest, such as temperature, pressure, voltage, battery level, light, motion, sound, distance to objects, etc., and to operate in some process in response to some control signals received from a controlling node, to mention a few illustrative examples. An MTC device may further be installed at a fixed location or on a moving structure such as a vehicle. Especially in the latter case, the radio conditions may change rapidly for the MTC device.
The MTC devices may be wirelessly connected to a serving network node of a radio network to report data comprising information about their measurements and observations to the controlling node. The controlling node may further send various commands and instructions back to the MTC devices to control their operation.
An example of an arrangement with multiple MTC devices is schematically illustrated in FIG. 1 where the MTC devices “D” are operatively installed at different locations in an area 100, the MTC devices D being configured to send reports “R” over a radio network 102 to a controlling node 104. The controlling node 104 may also send various commands “C” to different MTC devices D.
As mentioned above, it is of interest for network operators to improve capacity in their networks by utilizing the available radio resources as efficiently as possible. It may also be of interest to ensure reliability when data is transmitted to or from the wireless devices, e.g. MTC devices, to avoid that too much errors occur in the information communicated, if required. It may also be of interest to ensure low latency when data is transmitted to or from the wireless devices, e.g. MTC devices, if required.
If a data receiving node detects that data has not been received correctly from a data sending node, the data receiving node may according to conventional procedures send a feedback message effectively indicating an error, back to the data sending node which then may retransmit the same data to the data receiving node. The retransmission may be repeated, e.g. until the data has been received correctly which is confirmed by another feedback message from the data receiving node indicating correct reception. However, such feedback signaling adds delay to the communication which may not be acceptable, e.g. when the data rapidly becomes out of date and therefore useless at the data receiving node. It may thus happen that the data is not successfully received and decoded in time and cannot therefore be used, in spite of one or more retransmissions which have in this case been performed to no avail while still consuming radio resources. The feedback signaling also consumes additional radio resources and may further generate additional interference in the network.
MTC communication is thus used for establishing communication between machines and between machines and humans. The communication may involve exchange of data, signaling, measurement data, configuration information, etc. The MTC devices are quite often used for applications such as sensing environmental conditions (e.g. temperature reading), metering or measurement of various parameters (e.g. electricity usage), fault finding or error detection, etc. There are several MTC use cases that can be classified into two broader groups depending on their requirements, referred to as “massive MTC” and “critical MTC” or C-MTC for short. For massive MTC, low cost and enhanced coverage are desirable aspects while latency and reliability are typically more significant aspects for the critical MTC.
Cost reduction can be realized by relaxing the requirements on peak rate and receiver performance in a network where Long Term Evolution, LTE, is employed. LTE Release 12 introduces a low cost UE category called UE category 0 with a relatively low peak rate of 1 Megabits per second, Mbps, and relaxed performance requirements that can be fulfilled having just a single antenna receiver in the UE. The cost can be further reduced by supporting only half duplex FDD (Frequency Division Duplex) capability instead of full duplex FDD capability. The latter feature avoids the need for having duplex filter since the UE never transmits and receives at the same time in half duplex FDD. The cost can further be lowered by reducing the current RF (Radio Frequency) bandwidth for LTE UEs from 20 MHz to 1.4 MHz or even to 200 KHz.
MTC devices for LTE are sometimes required to support enhanced UL (Uplink) and/or DL (Downlink) coverage. The enhanced coverage may also be interchangeably called extended coverage. These devices are installed at locations where path loss between the MTC device and the base station can be very large such as when the MTC device is used as a sensor or metering device located in a remote area such as a basement of a building. In such scenarios correct reception of signals from the base station may be quite difficult to achieve. For example, the path loss can be greater than 15-20 dB compared to normal operation. In order to overcome such difficulties, it would be helpful to substantially enhance the coverage in uplink and/or in downlink. This can be realized by employing one or more techniques in the UE and/or in the radio network node for enhancing the coverage, e.g. by boosting of DL transmit power, boosting of UL transmit power, enhanced UE receiver, signal repetition, etc.
For critical MTC, other requirements such as latency and/or reliability are typically of importance. The latency requirements may be in the order of 1-10 ms end-to-end at the same time as the reliability requirements, e.g. defined as guaranteed packet delivery within a given time limit, can be as stringent as a packet delivery error rate not exceeding 10−9. In many use cases, a mix of applications sharing the same air interface such as in a factory can be envisioned with some applications having stringent requirements and other applications having more relaxed requirements.
Today's wireless interfaces typically operate at 10−1 reliability and delays in the order of tens of milliseconds, ms. Techniques that may be used to achieve this reliability include an appropriate choice of modulation and coding scheme to match the signal quality (link adaptation) and power control. Also, a feedback loop may be employed where a negative acknowledgement, NACK, or the absence of an acknowledgement within a given time indicates the need for a retransmission which is then scheduled later in time.
It may thus be a problem that the above-mentioned requirements for low latency and high reliability, e.g. in critical MTC, may not be met when transmitting data blocks to a receiving radio node, in either uplink or downlink. In that case, the transmitted data blocks may be more or less useless for the receiving radio node which naturally may affect the operation of the receiving radio node negatively. Furthermore, precious radio resources have thereby been wasted to no avail, and interference may also have been generated by such pointless transmission which could potentially be harmful to other transmissions in the radio network and the overall capacity in the network.